feat(invoices): per-line percentage discount and separate fakturamarkning (#2084)

* feat(invoices): per-line percentage discount and separate fakturamarkning

User request: rabatt i procent per artikelrad, and a marking field
separate from Er referens.

- invoice_items.discount_percent (0-100, default 0): line_total and
  vat_amount are stored NET of the discount. Shared exact-ore math in
  lib/invoices/line-amounts.ts (gross, discount, net) used by the web
  builder, staged-operation commit, editor preview, PDF, and Peppol.
  Undiscounted lines keep the legacy unrounded qty*price byte-identical.
- ROT/RUT deduction computes on the discounted net line total.
- invoices.invoice_marking: printed on the PDF next to the references
  and mapped to Peppol BT-10 BuyerReference (marking wins over
  your_reference; either satisfies the BT-10 requirement).
- Peppol renders the discount as a BG-27 line AllowanceCharge
  (reason code 95, MultiplierFactorNumeric, Amount, BaseAmount).
- Editor: "Lagg till rabatt" in the row menu (same reveal pattern as
  ROT/RUT), Markning row next to Er referens, forval chip, review
  dialog shows discounts and marking.
- Plumbed through v1 REST projections, MCP create/get/update invoice
  tools, pending-operations update path, and copy-invoice (discount
  copied; marking deliberately not, it is recipient-specific).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JJAt9yM7tgZ69f1XnNnq52

* fix(invoices): carry discount_percent through every deduction, credit, convert and preview path

Skeptic + CI findings on the discount/marking feature, one pass:

- generateRotRutLines and propose-send-lines now pass discount_percent
  into computeDeduction: the send/credit/cash verifikat booked 1513 on
  the GROSS line while deduction_total, the PDF and the Skatteverket
  claim carried the net, stranding the difference on 1513 and pushing
  1510 negative once the customer paid. Test pins 1513=3000/1510=7000
  for a 20%-discounted 10 000 kr ROT line.
- preview-pdf route accepts discount_percent (net totals + net-based
  deduction) and invoice_marking; the editor now sends the marking, so
  the preview equals the invoice it becomes.
- Credit notes carry discount_percent (buildCreditNoteItem, v1 credit
  route select+insert, MCP credit executor) and invoice_marking, so the
  kreditfaktura face arithmetic multiplies out and shows the Rabatt
  column (ML 17 kap 24 §).
- Proforma->invoice convert copies discount_percent + invoice_marking:
  the converted invoice previously failed Peppol LINE_TOTAL_MISMATCH
  and lost the rebate on the next builder pass.
- Editor hides the discount menu in self-billed mode (the self-billed
  wire shape has no discount; previewed net would book gross).
- MCP staging and commitCreateInvoice reject a non-number
  discount_percent (a string coerced past the range check but was
  ignored by the totals math and still stored).
- Regenerated skills/accounted-api (apiskill:check CI failure).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JJAt9yM7tgZ69f1XnNnq52

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

DECISIONS.md

@@ -1384,6 +1384,7 @@ One line per decision: `[YYYY-MM-DD] <decision>: <why>`. Appended by agents and
 [2026-08-31] Login/register methods come from GoTrue (/auth/v1/settings + admin customProviders) instead of app-side flags; NEXT_PUBLIC_GOOGLE_AUTH_ENABLED removed (PR #1869): the Supabase dashboard becomes the single switch, an allowlist of auth-js provider ids filters non-login entries like anonymous_users, and hosted rendering is unchanged because Google is enabled in prod GoTrue. The Vercel env var stays set for old-build rollback safety; delete it after a few deploys.
 [2026-08-31] Single prominent amount is PROMOTED into editable totals.total (totalSource='prominent') instead of living in a read-only Belopp row: Emil's call, an uncorrectable load-bearing value violated the prefill-override-editors rule. Provenance keeps matching fallback-grade (discount, date guard, hunt exclusion); a user edit of TOTALT clears the stamp. Multi-amount docs keep the Belopp row: promoting one of several figures would invent a total.
 [2026-08-31] Image-scan red fixed by bumping the node:22-alpine digest (alpine 3.23 to 3.24.1), not by widening the gate: the Dockerfile's apk-upgrade layer is frozen by the GHCR buildx layer cache, so a fix published after the last cache-busting change (libssl3 3.5.8-r0 for CVE-2026-14456) never reaches the published image until the FROM digest moves; the red scheduled scan is the designed alarm for exactly this bump. cron.Dockerfile gained the same apk upgrade (it had none).
+[2026-08-31] Per-line discount stores NET line_total via computeLineNet (roundOre(gross) minus roundOre(gross*d/100)) rather than round(gross*(1-d/100)): the subtracted-rounded-discount form keeps gross = discount + net exact in ore arithmetic, which the Peppol BG-27 line allowance (Amount + LineExtensionAmount = BaseAmount) and the PDF discount column both need; undiscounted lines keep the legacy unrounded qty*price so existing invoices and the Peppol LINE_TOTAL check stay byte-identical. ROT/RUT deducts on the discounted net (the customer pays that). invoice_marking is deliberately NOT copied by copy-invoice (recipient/PO-specific, same rule as your_reference) and NOT added to recurring schedules (follow-up if requested).
 [2026-08-31] Own-company-as-supplier guard nulls the supplier block instead of flagging or substituting the issuer: an empty LEVERANTOR is always safe, a guessed issuer is not; BYO/agent-supplied extraction paths are deliberately exempt (explicit input, not a model misread).
 [2026-08-31] gnubok-home-ok cache cookie is user-scoped (userId~host) instead of cleared on sign-out: sign-out happens client-side via supabase.auth.signOut so no server surface reliably sees it, while a value bound to the session's user makes any inherited verdict miss the cache by construction. Separator ~ because it is unreserved under encodeURIComponent AND a legal raw cookie octet, so the value round-trips identically whether or not the cookie layer percent-encodes. Old host-only cookies never match and self-heal; found via the amnas account-switch repro (two logins 9 s apart shared the verdict).
 [2026-08-31] Bookkeeping digest email is per-user per-COMPANY per-day (not one aggregated mail across companies): notification_log.company_id anchors the claim, subject lines stay unambiguous, and most users have one company; consultants can opt in and get one short mail per client. Window is a fixed last-24h (cron cadence) rather than tracking last-sent state. Settings toggle stays hardcoded Swedish like the rest of the push-notifications extension UI (no next-intl wiring in extension components); revisit if that surface is ever translated.